This contract supports activities related to the Biomarker Validation Study of Internet-based and Conventional Self-report Instruments for Assessing Diet and Physical Activity within the NIH-AARP cohort. This study is one component of a multi-center biomarker validation study project to be carried out within as many as 3 other large cohorts in the United States to evaluate measuremtn error structure of the assessment instruments. This study will also provide a unique scientific opportunity to evaluate the heterogeneity of the measurement error structure across mulitple and diverse study populations.